Copolymerization of trioxane with an epoxy-containing comonomer in the presence of formaldehyde



United States Patent 3,397,181 COPOLYMERIZATION OF TRIOXANE WITH ANEPOXY-CONTAINING COMONOMER IN THE PRESENCE OF FORMALDEHYDE George W.Halek, New Providence, and Frank M.

Berardinelli, South Orange, N.J., assignors to Celanese Corporation, NewYork, N.Y., a corporation of Delaware No Drawing. Continuation-impart ofapplication Ser. No. 353,588, Mar. 20, 1964. This application Mar. 8,1967, Ser. No. 621,448

8 Claims. (Cl. 260-67) ABSTRACT OF THE DISCLOSURE Trioxane iscopolymerized with an epoxy-containing comonomer in the presence offormaldehyde in order to reduce the induction period.

CROSS-REFERENCE TO RELATED CASES The present application is acontinuation-in-part of application Ser. No. 353,588, filed Mar. 20,1964, and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION The present invention relates to thecopolymerization of trioxane with a minor amount of at least oneepoxycontaining comonomer to produce a strong, stable plastic material.More particularly, the invention relates to the achievement of morerapid copolymerization in such processes by elimination or substantialreduction of a prepolymerization induction period.

It has previously been disclosed that in some instances when trioxane ishomopolymerized, a period of time elapses from when the catalyst orinitiator is added to the system to when polymerization of the trioxaneto high polymer begins. See, for example, Kern et al., AngewandteChemie, vol. 73(6), Mar. 21, 1961, pp. 177-186. This time lapse has beenreferred to as an induction period, during which it is believed that thedepolymeri'zation of trioxane to formaldehyde occurs to the essentialexclusion of trioxane polymerization. The trioxane polymerization itselfbegins only 'When the formaldehyde has attained a given equilibiumconcentration or amount, which varies with the polymerization reactiontemperatures employed.

Ideally, the induction period is as close to zero time as possible suchthat trioxane polymer formation begins the instant the catalyst is addedto the polymerization zone or system.

In order to eliminate or minimize the induction period in the trioxanehomopolymerization it has been suggested that extraneous formaldehyde beadded to the system, preferably in an amount equal to the equilibriumconcentration. Thus, when the polymerization catalyst is introduced intothe polymerization zone, trioxane polymerization begins immediately.

It has now been found that in addition to the induction period which mayor may not occur when trioxane is homopolymerized, a further inductionperiod, sometimes hereinafter referred to as a secondary inductionperiod, occurs when trioxane is copolymerized with an epoxycontainingcomonomer. In other words, the secondary induction period is in additionto what may be referred to as the primary induction period. Thus, evenif the above-mentioned equilibrium concentration of formaldehyde isadded to eliminate the primary induction period, the secondary inductionperiod will still occur.

During the secondary induction period, as in the pri- 3,397,181 PatentedAug. 13, 1968 mary period, essentially no polymerization of trioxane tohigh polymer occurs. It has also been found that the length of thesecondary induction period increases with increasing concentration ofepoxy-containing comonomer in the reaction mixture. The inductionperiods result in inefficient use of the reaction space and necessitatelarger reactors for a given amount of product in a given time.

SUMMARY OF THE INVENTION Accordingly, the primary object of the presentinvention is to eliminate or substantially reduce the secondaryinduction period.

Another object of this invention is the provision of an efficient andsimple method for carrying out the copolymerization of molten trioxanewith an epoxy-containing comonomer, which may be readily effected in acontinuous process.

Other objects of this invention will be apparent from the followingdetailed description and claims. In this description and claims allproportions are by weight unless otherwise indicated.

In accordance with the present invention trioxane is copolymerized withan epoxy-containing comonomer in the presence of a copolymerizationcatalyst in a copolymerization zone, wherein is introduced extraneousformaldehyde in an amount greater than that which is necessary toeliminate any primary induction period.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is important to understandthat the so-called primary induction period which may occur duringtrioxane homopolymerization also may occur during trioxanecopolymerization. The present invention, however, is directed to theelimination or substantial reduction of the secondary induction period,which always occurs when trioxane is copolymerized with an epoxycompound. Therefore, the formaldehyde is added to the system in anamount in excess of that needed to satisfy or eliminate the primaryinduction period, whenever it occurs.

The secondary induction period occurs only when an epoxy compound iscopolymerized with the trioxane and is believed to be due to the epoxycompound acting as a formaldehyde scavauger. The epoxy compound causesthe trioxane to depolymerize to formaldehyde which then reacts with theepoxy ring. This depolymerization continues to occur until there is amol of formaldehyde for each epoxy ring or equivalent present in thesystem.

The number of mols of formaldehyde introduced into the polymerizationzone per epoxy ring or equivalent present therein is desirably at leastabout 0.1. Amounts over about 0.5 mole are more effective, and bestresults are obtained when there is employed at least about 1 mol, e.g.,1.1 to 6 mols of formaldehyde per epoxy ring or equivalent. It is to beunderstood that the above mol figures are in addition to the mols offormaldehyde that are necessary to eliminate the primary inductionperiod, when it occurs.

The equilibrium concentration or amount of formaldehyde necessary toeliminate the primary induction period may be determined by simpleexperimentation as Well known to those skilled in the art, for example,by conducting a trioxane homopolymerization run under the sameconditions that are to be used in the copolymerization and measuring theamount needed.

The copolymerization conditions of temperature, pressure, type ofcatalyst, comonomer concentration and the like are similar to thosenormally used in the copolymerization of trioxane with epoxy-containingcomonomers, for example, as described in Walling et al. US. Patent No.3,027,352, which is assigned to the assignee of the present invention.Other patents describing similar copolymerizations of trioxane andepoxides or epoxy compounds are British Patent No. 905,828; FrenchPatent No. 1,319,178, of Fisher, Brown and Heinz; and South AfricanPatent No. 62/4,47l of Heinz and McAndrew, the disclosures of which areincorporated herein by reference.

Suitable catalysts for the copolymerization of trioxane and oxirane(epoxy) compounds are well known in the art, and any of these may beemployed in the practice of the present invention. Preferred catalystsof this type are cationic. As is known in the art the catalyst may begenerated in situ by the action of radiation on ingredients of thereaction mixture which are non-catalysts in the absence of suchradiation; one class of such activatable noncatalysts includes thelightor heat-activatable aryldiazonium fiuoborates described in BelgianPatent No. 593,648 of Farbwerke Hoechst. The amount of catalyst usuallyused in the copolymerization process is between about 1 ppm. and about10 ppm. based on the weight of the reactant mass, Boronfluoride-containing catalysts are usually used in amounts between about1 p.p.m. and about 10 ppm. and preferably in amounts between about 10p.p.m. and about 10 p.p.m.

It is preferred to carry out the copolymerization of this invention inthe liquid state, most preferably using molten trioxane wherein themolten trioxane constitutes the major portion, generally about 80percent or more of the reaction mixture. However, it is within the scopeof this invention to employ solid-state copolymerization.

Generally, the temperature of the copolymerization reaction will be inthe range of about to about 115 0, preferably in the range of about 60to about 90 C.

It is to be understood that the term copolymer as used herein includesterpolymers and higher copolymers. In addition, more than one type ofepoxy-containing comonomer may be copolymerized with the trioxane.Comonomers containing no epoxy rings or equivalents may also be employedas long as at least one of the comonomers used contains an epoxy ring orrings.

Illustrative of the epoxy-containing comonomers or compounds which maybe used in the present invention are ethylene oxide; 1,2-propyleneoxide, vinyl cyclohexene dioxide (l-epoxyethyl, 3,4-epoxycyclohexane),which is a di-epoxypropane, since it has two groups; cyclohexane oxide;styrene oxide; 3,4-epoxyvinyl cyclohexane; butadiene dioxide; butadienemonoxide; resorcinol diglycidyl ether; butanediol diglycidyl ether;diglycidyl ether; allyl glycidyl ether; phenyl glycidyl ether;trimethylolpropane triglycidyl ether; dicyclopentadiene dioxide;dipentene dioxide; isobutylene oxide; indene oxide; butylene oxide;octylene oxide and other alkylene oxides; or 1,4-dihydronaphthaleneoxide. The epoxy-containing comonomer may also contain non-hydrocarbonsubstituents; for example there may used compounds containing halo,nitro, or nitrogenous heterocyclic, or carboxylic ester substituents,such as epichlorohydrin and other epihalohydrins; pentachlorophenylglycidyl ether; paranitrophenyl glycidyl ether;ethyl-fi-methyl-fi-phenyl glycidate; trichloromethyl ethylene oxide;u-phenyl-achloromethyl ethylene oxide; 3-piperonyl-l,2-epoxypropane; or4-bromo-1-naphthyl ethylene oxide.

Generally, ethylene oxide is more reactive toward trioxane than any ofthe other above mentioned epoxy compounds. Thus, it is preferred to useethylene oxide as the sole epoxy compound or to use the other epoxycompounds in association with a second, more highly reactive, comonomersuch as ethylene oxide or a cyclic formal such as 1,3-dioxolane. Aparticular useful combination of properties is obtained by the use of ablend of a major amount of trioxane, a small amount of a polyfunctionalepoxy-containing compound having two copolymerizably reactive groups anda minor, but larger, amount of a second, highly reactive, comonomer ofthe type mentioned in the preceding sentence.

As mentioned above, other types of comonomers may also be used such asother cyclic ethers, e.g., formals such as dioxolane or pentaerythritoldiformal, or oxetanes such as trirnethylene oxide; lactones such asgamma-butyrolactone or propiolactone; cyclic anhydrides such as adipicanhydride; cyclic carbonates such as ethylene glycol carbonate or othercomonomers known to the art, e.g., vinylidene compounds such as styreneor vinyl isobutyl ether. It is advantageous to limit the total amount ofcomonomers employed, including both epoxyand non-epoxycontaining types,so that the oxymethylene content of the resulting copolymer is at leastabout percent, preferably, at least about percent.

In general, the proportions of total comonomer employed may be, forexample, the same as those used in the Walling et al., Heinz et al. andFisher et al. patents previously mentioned. Preferably about 0.5 to 10percent, based on the weight of the trioxane, of epoxy-containingcomonomer is used, more preferably 0.5 to 5.0 percent. Thecopolymerizable composition may contain suitably 0.01 or more epoxyequivalent per mol of trioxane, more desirably about 0.02 to 0.1 (e.g.0.04) epoxy equivalent per mol of trioxane.

Upon completion of the copolymerization reaction to the desired degree,the reaction mixture is usually deactivated by neutralizing thecatalyst. A satisfactory method of deactivating the reaction mixture isby washing in an excess of a solution of tributylamine in acetone. Thecopolymer may then be recovered by successive washings and filtrationsin acetone, followed by air drying.

If desired the copolymer may be given a thermal treatment or ahydrolysis or alcoholysis treatment such as is described in US. PatentNo. 3,103,499 and South African Patent No. 61/ 1,726, the entiredisclosures of which are incorporated herein by reference. The productof such treatment may be further stabilized by the addition of chemicalstabilizers known to the art, such as are described in British PatentNo. 951,272, Belgian Patent No. 603,786 and French Patents Nos.1,330,587 and 1,338,054.

As shown in the following examples it is convenient to blend theformaldehyde with the trioxane before the addition of comonomer andcatalyst. Other methods of addition may of course be employed. Thus theformaldehyde may be blended with the comonomer or with a blend of thecomonomer and trioxane. Externally generated formaldehyde may even befed to the copolymerizable reaction mixture after the addition of thecatalyst, continuously or batchwise. It is preferred, ,however, to addthe formaldehyde to the copolymerization zone or system prior to theaddition of the catalyst, as the induction period starts uponintroduction of the catalyst or initiator.

It is important to realize that the present invention contemplates theintroduction of extraneous formaldehyde from any source into the mixtureor blend of trioxane and epoxy-containing comonomer.

The invention is additionally illustrated by the following examples.

Example I 40 parts by weight of pure molten trioxane was placed in eachof two equivalent glass reaction tubes and maintained at 65 C. out ofcontact with the atmosphere. To one tube (18) was added 1.5 parts (1.25moles/liter of reaction mixture) of anhydrous formaldehyde gas obtainedby pyrolyzing alpha-polyoxymethylene and passing it through two trapsmaintained at -15 C. and a cyclohexane scrubber. The rubber caps of bothtubes were then replaced by metal bottle caps lined with neoprene andTeflon gaskets. 0.9 part (2.2 weight percent) (0.50 mole/liter ofreaction mixture) of ethylene oxide liquid was injected into each tubeand the tubes allowed to come to temperature equilibrium in a 65 C. oilbath. 0.0024 part of boron fluoride dibutyl etherate dissolved in 1.6parts by weight of dry cyclohexane was injected into each tube (1A, notcontaining added formaldehyde; and 1B, containing 1.5 parts of addedformaldehyde). This represents 20 p.p.m. of catalyst, calculated as BFBoth tubes were then rotated at 65 C. Tube 1A remained clear for 55minutes and then became cloudy; it became milky 35 minutes later;another 50 minutes later it was removed and its contents deactivatedwith a solution of tributylamine in acetone. Tube 1B was similarlyobserved. It became cloudy as soon as the catalyst was added, was milky35 minutes later; another 55 minutes later it was removed and itscontents deactivated with the same deactivation solution. After threewashes and filtrations from acetone, tube 1A yielded a copolymer havingan I.V. (0.1 g./ 100 cc. 98/2 p-chlorophenol/ alpha-pinene) of 1.9. Tube1B yielded a copolymer of 2.0 I.V.

Example II The procedure of Example I was repeated except that 0.0060part of boron fluoride dibutyl etherate (50 p.p.m. BF was added to eachtube. The no-formaldehyde tube (2A) was initially clear but became milkyat 15 minutes and turned solid 9 minutes later. Theformaldehyde-containing tube (2B) turned milky at 10 seconds and wassolid at 30 seconds. After being worked up, tube 2A yielded a copolymerwith an I.V. of 0.8, and tube 2B yielded a copolymer with an I.V. of0.8.

Example III (a) To 450 parts of purified molten trioxane in a N purgedflask was added 8.8 parts (0.65 mole/liter of reaction mixture) offormaldehyde generated as per Example I. The clear solution wastransferred to a stainless steel sigma-blade mixing reactor and sealedoff. 8.9 parts (0.45 mole/liter of reaction mixture) of liquid ethyleneoxide was injected and the system stirred. Analysis of 25 ml. of themixture showed 8.8 parts of free CH O/450 parts of batch to be present.Analysis of another 10 ml. sample of the mixture (still clear) bytitration showed 8.9 parts of ethylene oxide/450 parts of batch to bepresent. 0.06 part of boron fluoride dibutyl etherate (50 ppm. BF in15.6 parts dry cyclohexane was injected at 63 C. and the temperature ofthe middle of the batch observed by a potentiometer thermocouple. Aninitial 10 C. exotherm peaked at 0.7 minute and initial exotherm periodof 13 minutes (compared to 1.7 minutes for the CH O-oOntainingexperiment). The major exotherm then began and the product was removedto the deactivating solution 10 minutes after the peak temperature hadbeen reached.

The two products were worked up as in Example I. They were thenhydrolyzed in a 10 percent solution of dimethyl formamide/benzyl alcoholpercent volume/ 50 percent volume containing tri-n-butylamine in theamount of 1 percent of the polymer weight. Product III(a) retained 82.3percent of its weight for an overall yield of 75 percent. Control III(b)retained 85.3 percent of its weight for an overall yield of percent. Thebydrolyzed polymers, no-formaldehyde and formaldehydecontainingrespectively, had the following characterizing properties: I.V. 0.9;1.0; melt index 53, 29; 10x/x ratio 1 23, 19; ethylene oxide totalpercent and ratio of mono:di:trimeric ethylene oxide units 2.60,58:31:11; 2.54, 59:31:10.

Both hydrolyzed products were stabilized with 0.1 percent cyanoguanidineand 0.5 percent CAO5 3 in a Plastograph at 190 C. for 7 minutes. Theythen exhibited K values of 0.013 and 0.012 (no-CH O, CH O).

Both products were compression molded into 125 mil Examples IV to VIIIIn each of these examples 40 parts by weight of trioxane wascopolymerized with ethylene oxide in the amount shown in Table I, belowexcept for Example VIII, where trioxane was homopolymerized. Thepolymerization reaction was carried out at C. in the presence of boronfluoride dibutyl etherate as the catalyst. The catalyst was dissolved in1.6 parts by weight of cyclohexane and is reported in Table I in termsof parts per million of reaction mixture based on boron fluoridecontent.

Formaldehyde was added in Examples IV and VI in the amount shown inTable I by generation from alpha polyoxymethylene. The time it took forthe reaction mixture to become cloudy, and the time it took for thereaction mixture to become a thick slush were observed and are shown inTable I.

dropped 3.0 C. at 1.7 minutes. The temperature drop indicated the end ofthe induction period. The temperature then rose to a 30 C. exotherm andthen dropped 2.5 minutes later, indicating that the maincopolymerization had occurred. The product was removed 10 minutes laterto the deactivating solution.

(b) A control experiment using the same batch of trioxane was conductedby the same procedure except that the formaldehyde addition was omitted.Analysis for free formaldehyde just before addition of catalyst was 6percent. The ethylene oxide analysis was 8.9 parts/ 450 part batch.Addition of catalyst was followed by an TABLE I Moles oi Wt. ofWtEplenient FWt. of1 golilmgl- C t I t gimetln E is Eth lane of t yeneormae y e, a ays inu es 1 1 2? Oiiide Oxlde dehyde Moles or (p.p.m.)

Ethylene Cloud Slush Oxide Example IX 65 This example illustrates theuse of formaldehyde to decrease the induction period in the productionof polymers of trioxane and a compound containing a plurality of epoxygroups, here specifically vinyl cyclohexene dioxide l-epoxyethyl3,4-epoxycyclohexane The 10w/w ratio is the ratio between the weight offlow through a standard melt indexer at standard load and the weight offlow through the same melt indexer at ten times the standard load (bothat standard conditions).

2 KDaao values are the average percent of polymer degraded per minutewhen the polymer is maintained at 230 C. in an open vessel in acirculating air oven for 45 minutes.

2,2-rnethylene-bis(l-methyl, G-tertiary butyl phenol).

To 1000 grams of molten trioxane there was added gaseous anhydrousformaldehyde until the formaldehyde content of the trioxane was 1.34percent. A solution of grams of vinylcyclohexene dioxide in grams ofcyclohexane was added, followed by 20 grams of ethylene oxide. Then 0.22gram of boron fluoride di-n-butyl etherate dissolved in 20 grams ofcyclohexane were added, all while the reaction mixture was maintainedwith stirring at 65 C. by maintaining the reaction flask in a constanttemperature bath, also at 65 C. The temperature of the reaction mixture(still maintained in the constant temperature bath) rose to 75 C. 4minutes after the catalyst was added, In another minute the reactionmixture became light yellow in color. 6.5 minutes after the caltalystwas added the reaction mixture had become very turbid due to formationof polymer. Analysis of the reaction mixture four minutes after theaddition of the catalyst showed that only 18 percent of the originaloxirane content was present.

In contrast, when similar conditions were used except that noformaldehyde was added, the induction period for the clear mixture toturn turbid was about 21 minutes and the oxirane content even after 14minutes was about 60 percent of the original oxirane content.

As can be seen from Example VIII there was generally no induction periodin the catalytic homopolymerization of molten trioxane. Other workers(e.g. Okamura, Tomura and Tomikawa in Kogyo Kagaku Zasshi, vol. 65, No.5 (1962) pages 712-716) have reported a similar absence of a substantialinduction period in the catalytic homopolymerization of trioxane insolution. Under some conditions, however, there may be an inductionperiod during homopolymerization (as reported by Kern and Jaacks in I.Polymer Science 48 (1960) pages 399-404). It is within the scope of thepresent invention, although not preferred, to employ copolymerizationconditions under which, were the comonomers to be absent, there would bean induction period for the homopolymerization of trioxane. Aspreviously mentioned, when such a primary induction period does occurthe amount of formaldehyde added to the system must be greater than thatneeded to eliminate the primary induction period, the additionalformaldehyde being added in the amounts previously described.

The principle, preferred embodiment, and mode of operation of thepresent invention have been described in the foregoing specification.However, it should be understood that the invention which is intended tobe protected herein, may be practiced otherwise than as describedwithout departing from the scope of the appended claims.

We claim:

1. In the process for the copolymerization of trioxane, wherein trioxaneis copolymerized with at least one epoxycontaining comonomer and whereinthe copolymerization is effected in a copolymerization Zone in thepresence of a trioxane copolymerization catalyst, the improvement whichcomprises introducing extraneous formaldehyde into the copolymerizationzone in an amount greater than that which is necessary to eliminate anyprimary induction period that occurs under the conditions ofcopolymerization employed.

2. The process of claim 1, wherein the extraneous formaldehyde isintroduced into the zone so that it is present therein at the time ofintroduction of said catalyst.

3. The process of claim 2, wherein the amount of extraneous formaldehydeintroduced into said zone in addition to the amount necessary toeliminate any primary induction period is at least 0.1 mol offormaldehyde per epoxy equivalent present therein.

4. The process of claim 2, wherein said trioxane is molten and theamount of extraneous formaldehyde in troduced into said zone in additionto the amount necessary to eliminate any primary induction period is atleast about 1.0 mol of formaldehyde per epoxy equivalent presenttherein.

5. A process for reducing the secondary induction period which occursduring the catalytic copolymerization of trioxane with anepoxy-containing comonomer, which process comprises contacting a mixtureof the trioxane and the epoxy-containing comononer with extraneousformaldehyde in a copolymerization zone, said formaldehyde beingintroduced into said zone in an amount greater than the equilibriumconcentration of formaldehyde that is necessary to eliminate any primaryinduction period which might occur.

6. The process of claim 5, wherein the amount of epoxy-containingcomonomer present is the range of from about 0.5 to 10 percent, based onthe weight of the trioxane, and the amount of extraneous formaldehydeintroduced into the zone in addition to the amount necessary toeliminate any primary induction period is at least 1.0 mol offormaldehyde per epoxy equivalent.

7. The process of claim 5 wherein the trioxane is molten duringcopolymerization,

the epoxy-containing comonomer is ethylene oxide and is present in anamount in the range of from about 0.5 to 5 percent, based on the weightof the trioxane, and

the amount of extraneous formaldehyde introduced into the zone inaddition to the amount necessary to eliminate any primary inductionperiod is in the range of from 1.1 to 6 mols of formaldehyde per epoxyequivalent present therein.

8. The process of claim 7, wherein said formaldehyde is supplied asexternally generated gaseous anhydrous formaldehyde.

References Cited UNITED STATES PATENTS 3,337,507 8/1967 Gutweiler et al260-67 WILLIAM H. SHORT, Primary Examiner.

L. M. PHYNES, Assistant Examiner.

